This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-001832, filed Jan. 7, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a cooling unit for facilitating the radiation of heat from a heat generating component such as a semiconductor package, and also an electronic apparatus, such as a portable computer, which incorporates the cooling unit.
In recent years, various types of portable electronic apparatuses, as typified by notebook-sized portable computers or mobile information apparatuses, have been developed. Electronic apparatuses of this type each incorporate a semiconductor package for processing multimedia information such as characters, voices and/or images. The power consumption of semiconductor packages increases more and more in accordance with increases in processing speed and/or increasing number of functions incorporated therein. Accordingly, the amount of heat generated during the operation of the packages is rapidly increasing. Therefore, in order to secure reliable operation of the semiconductor packages, it is necessary to facilitate their heat radiation. To this end, various types of radiation/cooling means such as a heat sink, an electromotive fan for supplying cooling air, etc. are indispensable.
The conventional heat sink has a heat receiving portion for receiving heat generated from a semiconductor package, and a heat exchange portion thermally connected to the heat receiving portion. This heat sink is fixed on a circuit board with the semiconductor package mounted thereon.
If a gap exists between the heat receiving portion of the heat sink and the semiconductor package, it serves as a heat insulating layer and interrupts transmission of heat from the semiconductor package to the heat sink. To avoid this, in the prior art, a thermal conductive grease or a flexible thermal conductive sheet is interposed between the heat receiving portion of the heat sink and the semiconductor package to enhance the adhesion therebetween.
As a surface-mount type semiconductor package for use in a portable computer, a BGA-type semiconductor package is generally used. Where the BGA-type semiconductor package is mounted on a circuit board, it is possible that the thickness of the package on the circuit board will vary within a range of xc2x10.25 mm. Further, since an injection molded product of an aluminum alloy is used as the heat sink, a dimensional tolerance will inevitably occur. Accordingly, where the heat sink is secured to the circuit board, the thickness from the heat receiving portion to the circuit board may vary between different heat sink products.
In light of this, in the prior art, when a semiconductor package is thermally connected to the heat receiving portion of a heat sink by a thermal conductive sheet, the thickness of the sheet is set at a value that exceeds a maximum gap due to, for example, the dimensional tolerance of the heat sink. This enables the thick thermal conductive sheet held between the semiconductor package and the heat receiving portion to be forcibly elastically deformed so as to absorb variations in thickness between mounted semiconductor packages or the dimensional tolerance of the heat sink.
However, the thermal conductive sheet is generally formed of a rubber elastic member of a low density, and hence has a lower thermal conductance than a metal material. Therefore, in the conventional structure that requires the use of a thick thermal conductive sheet, a thermally-connected portion of the semiconductor package and the heat receiving portion will have a high thermal resistance. As a result, the heat of the semiconductor package cannot effectively be transmitted to the heat sink. In other words, there is room for improvement in enhancing the radiation of the semiconductor package.
It is the object of the invention to provide a cooling unit and an electronic apparatus, in which the adhesion of a heat generating component and a heat sink is kept high to enable effective transmission of heat from the heat generating component to the heat sink, and a thermal conduction path from the heat generating component to a heat exchange portion is formed thin and compact.
According to a first aspect of the invention, there is provided a cooling unit for cooling a heat generating component, comprising: a heat sink including a heat receiving portion for receiving heat generated by the heat generating component, and a heat exchange portion thermally connected to the heat receiving portion, the heat exchange portion being located adjacent to the heat receiving portion and separate from the heat generating component, the heat sink being movable toward and away from the heat generating component, the heat sink being urged by an elastic member toward the heat generating component; and ventilation means for sending cooling air at least to the heat exchange portion of the heat sink.
According to a second aspect of the invention, there is provided an electronic apparatus comprising: a housing; a heat generating component housed in the housing; a heat sink housed in the housing, and including a heat receiving portion for receiving heat generated by the heat generating component, and a heat exchange portion thermally connected to the heat receiving portion, the heat exchange portion being located adjacent to the heat receiving portion and separate from the heat generating component, the heat sink being movable toward and away from the heat generating component, the heat sink being urged by an elastic member toward the heat generating component; and ventilation means housed in the housing for sending cooling air at least to the heat exchange portion of the heat sink.
In the above-described structure, the heat of the heat generating component is transmitted to the heat receiving portion of the heat sink and then to the heat exchange portion of the same. Accordingly, the heat of the heat generating component is diffused over the entire heat sink and radiated to the outside of the heat sink. Heat diffusion and subsequent heat radiation is a natural cooling process. Since the ventilation means sends cooling air to the heat exchange portion, the heat exchange portion is forcibly cooled. Thus, the heat of the heat generating component is efficiently radiated from the heat exchange portion.
The heat receiving portion of the heat sink is movable toward and away from the heat generating component. If there is a variation in the thickness of the heat generating component or in the size of the heat sink, the movement of the heat sink can absorb the variation.
Moreover, since the heat receiving portion is always urged toward the heat generating component, the adhesion between the heat receiving portion and the heat generating component is kept high. Therefore, when providing a thermal conductive sheet between the heat receiving portion and the heat generating component, it is sufficient if the thermal conductive sheet has a thickness that enables the heat receiving portion and the heat generating component to be prevented from partially touching.
As a result, the thermal conductive sheet can be thinned to a required minimum limit.
Accordingly, the thermal resistance between the heat receiving portion and the heat generating component can be suppressed. This means that the heat of the heat generating component can be efficiently transmitted to the heat sink.
In addition, since, in the above-described structure, the heat receiving portion is not vertically parallel to the heat exchange portion, and the heat exchange portion is horizontally separate from the heat generating component, the thermal conduction path from the heat generating component to the heat exchange portion is formed horizontal. This enables the heat sink to be formed thin and hence to be easily incorporated in the housing.
According to a third aspect of the invention, there is provided a cooling unit for cooling a heat generating component, comprising: a heat sink including a heat receiving portion for receiving heat generated by the heat generating component, and a heat exchange portion thermally connected to the heat receiving portion, the heat exchange portion being located adjacent to the heat receiving portion and separate from the heat generating component; and an electric fan device for sending cooling air at least to the heat exchange portion of the heat sink, the electric fan device including a fan, a fan casing supporting the fan, and a heat sink support arranged adjacent to the fan casing.
The heat sink is pivotably supported by the heat sink support such that the heat receiving portion can move toward and away from the heat generating component, and the heat receiving portion is always urged by an elastic member toward the heat generating component.
In the above structure, if there is a variation in the thickness of the heat generating component or in the size of the heat sink, the variation can be absorbed by pivoting the heat sink. Further, since the heat receiving portion is always urged toward the heat generating component, the adhesion between the heat receiving portion and the heat generating component is kept high. Therefore, when providing a thermal conductive sheet between the heat receiving portion and the heat generating component, the thermal conductive sheet can be thinned to a required minimum limit. Accordingly, the thermal resistance between the heat receiving portion and the heat generating component can be suppressed, and hence the heat of the heat generating component can be efficiently transmitted to the heat sink.
In addition, in the above-described structure, the heat receiving portion is not vertically parallel to the heat exchange portion, the heat exchange portion is horizontally separate from the heat generating component, and the heat sink is not vertically parallel to the fan casing. Accordingly, the thermal conduction path from the heat generating component to the heat exchange portion is formed horizontal. This enables the cooling unit to be formed thin and compact.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.